Integrated circuit (IC) devices typically include an IC chip which is housed in a plastic, ceramic or metal "package". The IC chip includes an integrated circuit formed on a thin wafer of silicon. The package supports and protects the IC chip and provides electrical connections between the integrated circuit and an external circuit or system.
There are several package types, including ball grid arrays (BGAs), pin grid arrays (PGAs), plastic leaded chip carriers, and plastic quad flat packs. Each of the package types is typically available in numerous sizes. The package type selected by an IC manufacturer for a particular IC chip is typically determined by the size/complexity of the IC chip (i.e., the number of input/output terminals), and also in accordance with a customer's requirements.
FIGS. 1A and 1B show bottom and side sectional views of a typical BGA IC 100 including an IC chip 110 mounted on an upper surface 122 of a package substrate 120. Electrical connections between bonding pads of IC chip 110 and conductive lines (not shown) formed on substrate 120 are provided by bond wires 124. A plurality (twenty-five shown) of solder balls (sometimes referred to as solder bumps) 126 extend from a lower surface 128 of the substrate 120 which are electrically connected to the conductive lines. Electrical signals travel between each solder ball 126 and one bonding pad of IC chip 110 along an associated conductive line and bond wire 124. A cover 129, such as a cap or "glob top", is placed or formed over IC chip 110 and bond wires 124 for protection.
IC testing systems are used by IC manufacturers to test their ICs before shipping to customers. IC testing systems typically include a device tester, a device handler and an interface structure. A device tester is an expensive piece of computing equipment which transmits test signals via tester probes to an interface structure. The interface structure transmits signals between the leads of an IC under test and the device tester. A device handler is an expensive precise robot for automatically moving ICs from a storage area to the interface structure and back to the storage area.
FIGS. 2A and 2B show side and top views of a conventional interface structure 200 which is used to test BGA ICs. Interface structure 200 includes a disk-shaped printed circuit board (PCB) 210 and a contactor 300. PCB 210 includes groups of outer vias 212 which are spaced around the perimeter of PCB 210. The arrangement of outer vias 212 shown in FIG. 2 must be used with the SC212 tester from Credence Systems Corporation. Outer vias 212 are mounted onto and receive male tester probes extending from the device tester (not shown). Outer vias 212 are connected by metal traces (conductive lines) 230 to inner sockets 240 located in a central test area. Contactor 300 is mounted over the central test area such that pin terminals (discussed in further detail below) which extend from a lower surface of the of contactor 300 are received in the sockets 240. After a BGA IC is mounted onto contactor 300 by the device handler, the test device transmits test signals through the male tester probes (not shown) to the outer vias 212, and along traces 230 to the sockets, and finally through the contactor 300 to the BGA IC under test. Similarly, return signals from the BGA IC are transmitted to the test device through contactor 300, sockets 240, traces 230 and outer vias 212.
FIGS. 3A and 3B show a side sectional and top views of a contactor 300. Contactor 300 includes a housing 310 and a nesting member 320 movably mounted on housing 310 via support springs 330. Housing 310 includes lower wall 312, side walls 314 extending upward around the periphery of lower wall 312, and spring mounts 316 for receiving one end of the support springs 330. A peripheral edge of nesting member 320 is surrounded by outer side walls 314 of housing 310, thereby limiting horizontal movement of nesting member 320. However, a small gap G1 is provided between nesting member 320 and side walls 314 to allow vertical movement. Nesting member 320 includes a plate portion 322 positioned over the lower wall 312 of housing 310, and raised alignment walls 323 located at two comers of plate portion 322 which define a receiving area for BGA IC 100 (indicated in dashed lines). Plate portion 322 includes an indented area 324 having an upper surface 325, a lower surface 326, and a plurality of through-holes 328. Contactor 300 also includes a plurality of spring contacts 340 each having a C-shaped or S-shaped spring portion. Each spring contact 340 includes a contact portion 342 which extends through one of the through-holes 328 of nesting member 320, and a pin terminal 344 which extends through lower wall 312 of housing 310. When contactor 300 is mounted onto PCB 210, pin terminals 344 are received in sockets 240 formed in PCB 210.
Operation of conventional interface structure 200 is described with reference to FIGS. 4A and 4B. As shown in FIG. 4A, a device handler (not shown) places a BGA IC 100 (shown in silhouette) onto nesting member 320 with solder balls 126 extending into indented area 324. BGA IC 100 is aligned on nesting member 320 by contact between the peripheral edge of substrate 120 and raised alignment walls 323 of nesting member 320. This alignment is intended to position solder balls 126 over the contact portions 342 of the plurality of spring contacts 340. Subsequently, as shown in FIG. 4B, the device handler presses BGA 100 downward (in the direction indicated by arrow Z) against the force exerted by support springs 330. As nesting member 320 displaces downward, solder balls 126 move toward and abut contact portions 342. Further downward force is absorbed by the C-shaped or S-shaped portion of spring contacts 340. When the BGA IC is properly aligned, electrical signals are then transmitted between PCB 210 and BGA IC 100 through contact between solder balls 126 and the contact portions 342 of the plurality of spring contacts 340. The device handler then removes BGA IC 100, and nesting member 320 is biased into its original position by support springs 330.
Several problems are associated with conventional interface structure 200, and in particular, to conventional contactor 300.
First, contactor 300 is very expensive (approximately $500 or more), and also very fragile. Pin terminals 344 of spring contacts 340 are often bent or damaged when contactor 300 is mounted to PCB 210. Straightening or replacing bent pin terminals 344 is extremely time consuming and, therefore, IC testing system operators often discard damaged contactors. Further, due to their simple construction, spring contacts 340 typically weaken and fail after a relatively low number of test procedures. As a result, device testing using conventional interface structures is expensive and often time consuming.
A second problem associated with conventional interface structure 200 is described with reference to FIG. 4C. Nesting member 320 can become misaligned for reasons of temperature variation, aging, or manufacturing variation. When interface structures are mounted on device testers, this process is typically performed at room temperature. Subsequent testing procedures are often performed at much higher temperatures. This temperature difference causes deformation of spring contacts 340, which shift nesting member 320 horizontally relative to housing 310 (indicated in FIG. 4c by gap G2 which is larger than gap G1 shown in FIG. 3B). Because the device handler is adjusted to mount BGA IC 100 in the original (room temperature) position of nesting member 320, this shift results in a relative misalignment between BGA IC 100 and nesting member 320. Alternatively, due to repeated lateral motion when IC devices 100 are inserted and removed from nesting member 320, nesting member 320 may become permanently biased to one side. Or due to manufacturing inaccuracy, nesting member 320 may be misaligned from the beginning. In some cases, as shown in FIG. 4C, BGA IC 100 is mounted such that one corner is located on top of alignment wall 323. When this occurs, subsequent downward pressure by the device handler often destroys BGA IC 100. Therefore, unless this problem is quickly recognized and corrected, significant product loss can occur. One possible solution to this problem is to widen alignment wall 323 and provide a long, tapered surface such that BGA ICs slide easily into position on nesting member 320. However, because the overall width of contactor 300 is typically restricted, and because a portion of this width is occupied by side walls 314 of housing 310, the width of nesting member 320 (and, therefore, alignment wall 323) is limited.
A third problem associated with conventional interface structure 200 is described with reference to FIG. 4D. In particular, alignment within nesting member 320 is based on the outer peripheral shape of BGA IC 100. If the position of solder balls 126 relative to the outer edge of substrate 120 is shifted during package manufacturing, the resulting misalignment can result in total misalignment between contact portions 342 and solder balls 126, as shown in FIG. 4D.
Further, partial misalignment between balls 126 and contact portions 342 can cause BGA IC 100 to become wedged (stuck) to contact members 342. This situation is shown in FIG. 5A. As BGA IC 100 is pressed downward, the partial misalignment causes contact members 342 to slide along the outer sloped edge of solder balls 126, thereby causing deflection of contact members 342 against plate portion 322 surrounding through-holes 328. This wedging action can resist subsequent upward movement of BGA IC 100, thereby causing BGA IC 100 to become disengaged from the device handler, and causing a costly shut-down of the testing process.
A final problem associated with conventional interface structure 200 is described with reference to FIGS. 5B and 5C. In particular, because of the various alignment problems associated with conventional interface structure 200 (discussed above) it is required to utilize a relatively wide contact portion 342(1) shown in FIG. 5B, or a cup-shaped contact portion 342(2) shown in FIG. 5C to assure contact with solder balls 126. However, the flat upper surface 343 of contact portion 342(1) serves as a ledge upon which tin-lead contamination 344 from the solder balls deposits over a period of time. Similarly, the cup-shaped contact portion 342(2) collects tin-lead contamination 344. Tin-lead contamination 344 imposes a resistance between contact portions 342(1) and 342(2) and solder ball 126, thereby causing incorrect test results and the erroneous discarding of good parts.